Method and Device for Supplying a Space Propulsion Engine with Liquid Cryogenic Propellants

ABSTRACT

According to the invention, upstream of the injection means, the combustible propellant and the oxidant propellant are mixed at constant pressure; and to inject the said mixture of propellants at constant pressure into the combustion chamber ( 1 ), injection means ( 7  to  11 ) are chosen, making it possible to vary the flow rate of the said injected mixture.

The present invention relates to space propulsion engines supplied withcryogenic liquid propellants.

In known engines of this type, for example LOX-LH2 or LOX-keroseneengines currently used in launchers, the oxidizer propellant and fuelpropellant are injected separately into the combustion chamber of saidengines, the mixing of said propellants taking place in said combustionchamber.

Owing to the fact that, in these known engines, it is difficult to causerelatively large pressure variations in the propellant feeds withoutmodifying the ratio of the propellants in the mixture thereof, thepossible adjustment in thrust caused by such variations in feed pressureis relatively small. In practice, it is barely possible to obtain athrust adjustment of around 10 to 20%.

The object of the present invention is to remedy this drawback.

For this purpose, according to the invention, the method for supplyingthe combustion chamber of a space propulsion engine with cryogenicliquid propellants by injection means contained in an enclosure, isnoteworthy in that:

-   -   the fuel propellant and the oxidizer propellant are mixed at        constant pressure upstream of said enclosure so as to form a        mixture;    -   said mixture is fed into said enclosure via an orifice in the        latter; and    -   in order to inject said propellant mixture at constant pressure        from said enclosure into said combustion chamber, injection        means are chosen that enable the flow rate of said injected        mixture to be varied.

Thus, thanks to the present invention, the thrust of the engine can besubstantially varied by varying the flow rate of the injected mixture,without changing the feed pressure of said propellant injection means.Since the mixing takes place before injection, the fuelpropellant/oxidizer propellant ratio remains constant in the injectedmixture irrespective of the pressure drop of the mixture through saidinjection means and irrespective of the flow rate of the mixtureinjected by said means. Of course, as will be seen later, the variablegeometry of said injection means is designed so as to ensure a pressuredrop of the mixture sufficient to maintain, over a wide flow rate range,good combustion stability of said mixture in said combustion chamber.

Advantageously, the propellants are chosen to have similar liquefactiontemperatures and pressures. For example, the fuel propellant may beliquid methane, while the oxidizer propellant may be liquid oxygen.

For safety, upon operating said engine, the propellant mixture isignited inside said combustion chamber only after said mixture hasreached a supersonic velocity upon exiting the injection means.

To implement the method according to the present invention, it ispossible to use a device which comprises a fuel propellant tank, anoxidizer propellant tank and means for pressurizing said tanks to aconstant pressure, and in which:

-   -   means for mixing said fuel propellant with said oxidizer        propellant at constant pressure are provided upstream of said        enclosure;    -   communication means connect said mixing means to an orifice in        said enclosure; and    -   said injection means are capable of varying the flow rate of        said mixture injected at constant pressure.

Said injection means may include a plurality of needles, each of themcooperating with a calibrated orifice. Said plurality of needles may besupported by a first plate and the corresponding plurality of calibratedorifices may be made in a second plate, means being provided forimparting a relative movement between said first and second plateswhereby the distance therebetween is decreased or increased.

Advantageously, especially if the propellants have similar liquefactiontemperatures and pressures, said means for pressurizing the twopropellant tanks at constant pressure are common thereto.

In the usual case in which said engine includes a cooling circuit aroundsaid combustion chamber, it is advantageous for said mixture to be fedinto said enclosure via said cooling circuit.

Mixing means ensure that the two propellants are mixed turbulently. Saidmeans may be external to said engine and, in this case, it isadvantageous for them to be thermally coupled to a heat source, forexample the combustion chamber, making it possible to ensure that thetemperature of the mixture is such that, at the feed pressure of theinjection means, neither of said propellants passes into the solid phaseupon exiting said mixing means. Thus, according to a preferredembodiment, said cooling circuit around the combustion chamber itselfforms said mixing means.

Optionally, a pump may be provided for increasing the feed pressure ofthe propellant injection means, on condition that the propellant mixtureremains at a temperature guaranteeing that there can be no solid phasein the pipes.

The figures of the appended drawing will make it clearly understood howthe invention can be realized. In these figures, identical referencesdenote similar components.

FIG. 1 is a schematic partial view of a space propulsion engine and thedevice for supplying it with cryogenic liquid propellants, enabling thepresent invention to be illustrated.

FIG. 2 illustrates, in a view similar to FIG. 1, one embodiment of thepropellant mixing means.

FIG. 3 is a schematic partial view of the means for injecting thepropellant mixture, in accordance with the present invention.

FIGS. 1 and 2 show, schematically and partially, a space propulsionengine by its combustion chamber 1, which chamber is provided withpropellant injection means 2 and with a gas discharge nozzle 3 and iscooled by a peripheral cooling circuit 4.

The propellant injection means 2 comprise an enclosure 5 into which saidperipheral cooling circuit 4 runs at 6. The enclosure 5 communicateswith the combustion chamber 1 via a plate 7 provided with a plurality ofcalibrated through-orifices 8, for example distributed in concentriccircles or in rows and columns (see also FIG. 3). In addition, theenclosure 5 contains a plate 9 at least approximately parallel to theplate 7 and able to be moved closer to and further away from said plate7 (as indicated symbolically by the double-headed arrow F) thanks to anactuator 10, for example an actuating cylinder. The plate 9 has, on itsface turned toward the plate 7, a plurality of needles 11 placed incorrespondence with said calibrated orifices 8, so that each needle 11can cooperate with a calibrated orifice 8 in order to define the flowarea of said orifice. Of course, this flow area can be varied, under thecontrol of the actuator 10.

In addition, FIGS. 1 and 2 show an oxidizer (for example liquid oxygen)propellant tank 12, a fuel (for example liquid methane) propellant tank13 and a tank 14 containing an inert gas for pressurizing, in common andat constant pressure, said oxidizer propellant and said fuel propellant.

In the system shown in FIG. 1, the outlet lines 15 and 16 leaving thetanks 12 and 13 are joined to a mixer 17 external to the engine 1, 2, 3and capable of forming the mixture of said propellants and of sendingsaid mixture to the cooling circuit 4 via its outlet line 18.

The system shown in FIG. 2 does not include a mixer 17. Instead, theoutlet lines 15 and 16 leaving the tanks 12 and 13 are individuallyconnected to the cooling circuit 4 via calibrated orifices, 19 and 20respectively. In this case, the mixing of the propellants thereforetakes place in the cooling circuit 4.

In both cases, after the combustion chamber 1 has been cooled, thepropellant mixture penetrates the enclosure 5 at constant pressure andis injected with a variable flow rate into said combustion chamber 1 bythe injection means 7 to 11.

In light of the above explanations with regard to FIGS. 1 to 3, it wouldbe readily understood that the thrust P of the engine according to thepresent invention can be regulated by adjusting the flow rate of thepropellant mixture by the injection means 7 to 11, the pressure at whichsaid means are fed with said mixture remaining constant.

To initiate the combustion of the propellant mixture in the chamber 2(although the velocity of said mixture at the injection means issupersonic), an igniter (not shown) is provided, for example at thecenter or on the periphery of the plate 7.

Moreover, to spray the mixture and ensure stability of the combustion atfull power, each calibrated hole 8 in the plate 7 has a sufficientlyhigh length E/diameter ratio.

1-10. (canceled)
 11. A method for supplying the combustion chamber (1)of a space propulsion engine with cryogenic liquid propellants byinjection means contained in an enclosure (5), the method comprising:mixing the fuel propellant and the oxidizer propellant at constantpressure so as to form a mixture upstream of said enclosure (5); feedingsaid mixture into said enclosure (5) via an orifice (6) in the latter;and employing an injection means (7) to vary the flow rate of saidinjected mixture in order to inject said propellant mixture at constantpressure from said enclosure (5) into said combustion chamber (1). 12.The method as claimed in claim 11, wherein said propellants have similarliquefaction temperatures and pressures.
 13. The method as claimed inclaim 12, wherein the fuel propellant is liquid methane and the oxidizerpropellant is liquid oxygen.
 14. The method as claimed in one of claims11, wherein, upon operating said engine, said mixture is ignited insidethe combustion chamber (1) only after said mixture has reached the sonicvelocity upon exiting said combustion chamber.
 15. A device forsupplying cryogenic liquid propellants to a space propulsion engineprovided with a combustion chamber (1) into which said propellants areinjected by injection means included in an enclosure (5), said devicecomprising a fuel propellant tank (13), an oxidizer propellant tank (12)and means (14) for pressurizing said tanks (12, 13) to a constantpressure, wherein: means (17, 19, 20) for mixing said fuel propellantwith said oxidizer propellant at constant pressure are provided upstreamof said enclosure (5); communication means (4, 18, 19, 20) connect saidmixing means (17, 19, 20) to an orifice (6) in said enclosure (5); andsaid injection means (7 to 11) are configured to vary the flow rate ofsaid mixture injected at constant pressure.
 16. The device as claimed inclaim 15, wherein said injection means comprise a plurality of needles(11), each of them cooperating with a calibrated orifice (8).
 17. Thedevice as claimed in claim 16, wherein the plurality of needles (11) aresupported by a first plate (9), the plurality of calibrated orifices (8)are made in a second plate (7) and means (10) are provided for impartinga relative movement (F) between said first and second plates (9, 7)whereby the distance therebetween is decreased or increased.
 18. Thedevice as claimed in one of claims 15, for an engine that includes acooling circuit (4) around said combustion chamber (1), wherein saidpropellant mixture is fed into said enclosure (5) via said coolingcircuit (4).
 19. The device as claimed in one of claims 15, wherein saidmeans (17) for mixing the propellants are external to said engine. 20.The device as claimed in claim 18, wherein said cooling circuit (4)forms said mixing means.